A bipolar junction transistor (bipolar transistor or BJT) is a type of transistor that uses both electron and hole charge carriers. BJTs are manufactured in two types, NPN and PNP, and can be fabricated in integrated circuits. In operation, BJTs use two junctions between two semiconductor types: n-type and p-type.
The basic function of a BJT is to amplify current, which allows the BJT to be used as amplifiers or switches thus giving them wide applicability in electronic equipment including computers, televisions, mobile phones, audio amplifiers, industrial control, and radio transmitters. NPN BJTs also have wide range of applications in areas such as audio, linear and switching, high-voltage, and ESD device/circuits. One of the key objectives of high-voltage NPN transistors is for audio and low noise amplifiers. However, for a given base width, there is always a tradeoff between beta (e.g., collector current/base current) vs. BVCEO (breakdown between collector emitter with base open), as their product is usually a constant value.